Researchers have identified a genetic vulnerability in Quarter Horses which appears to put foals at greater risk of a dangerous form of pneumonia.
Rhodococcus equi is a bacterium that can cause severe pneumonia in young foals, often with fatal consequences.
The study team from Texas A&M University’s College of Veterinary Medicine and Biomedical Sciences said the genetic mechanisms that confer susceptibility and/or resistance to R. equi were not yet fully understood.
In previous work, the researchers identified a region on equine chromosome 26 which was associated with culture-confirmed clinical pneumonia.
They have now delved further, looking even closer at the makeup of the TRPM2 gene within this region, which was found to be associated with R. equi pneumonia.
The researchers, Cole McQueen, Canaan Whitfield-Cargile, Kranti Konganti, Glenn Blodgett, Scott Dindot and Noah Cohen, randomly selected 12 horses from 51 living at a Texas ranch where 17% of the foals born during 2011 came down with R. equi pneumonia.
They investigated in some detail the transcription of the target gene, the physiological role of which is not well understood. Transcription is the first step of gene expression, in which segments of DNA are copied into RNA, which are subsequently translated into protein.
The researchers, writing in BMC Genomics, said they identified differences in the way the gene was expressed, some of which contributed to susceptibility to R. equi pneumonia.
Cohen told Horsetalk: “We don’t have functional data, just that the different genotypes seem to have different transcripts, and it is possible that these different transcripts, termed splice variants, make a difference in this gene that is known to have a role in innate immune responses.
“There is precedent for splice variants in this gene influencing function, resulting in a more robust inflammatory response.
“Unfortunately, we haven’t been able to get funded to look at functional consequences of the variants. We think this work is important, not because we think there is a specific gene that explains R. equi pneumonia, which is a complex disease that has environmental and undoubtedly multiple genes that influence susceptibility.
“Rather, we think this work points to a major role for innate immune responses in determining the phenotype of infected foals, meaning whether or not they get the disease.
“But this is largely speculation based on the findings of this and other studies from our laboratory, and much more work needs to be done to strengthen the evidence.”
The study team said the data gathered in their research, to their knowledge, represented the first whole transcriptome assembly of the Quarter Horse genome.
Computer analysis indicated that more than 34,000 genes were present in the Quarter Horse genome.
TRPM2 SNP genotype previously associated with susceptibility to Rhodococcus equi pneumonia in Quarter Horse foals displays differential gene expression identified using RNA-Seq Cole M. McQueen, Canaan M. Whitfield-Cargile, Kranti Konganti, Glenn P. Blodgett, Scott V. Dindot and Noah D. Cohen.
BMC Genomics 2016 17:993 DOI: 10.1186/s12864-016-3345-3